The present invention relates generally to a coated article; and, more particularly, to a coated gas turbine component containing at least two adjacent cooling holes that are substantially uncoated.
In a gas turbine, pressurized air is mixed with fuel and ignited to generate hot pressurized gases. The hot pressurized gases pass through successive turbine stages that convert the thermal and kinetic energy from the hot pressurized gases to mechanical torque acting on a rotating shaft or other element, thereby producing power used for both compressing the incoming air and driving an external load, such as an electric generator. As used herein, the term “gas turbine” may encompass stationary or mobile turbomachines, and may have any suitable arrangement that causes rotation of one or more shafts.
The components exposed to the hot pressurized gases are typically hollow or contain a plurality of internal passages through which a pressurized fluid, such as compressed air, is caused to flow for the purpose of cooling the components. The cooling fluid typically exits to the flow of hot pressurized gases through a plurality of holes disposed within the component base material.
It is often advantageous to coat portions of the components with a coating to insulate the base material from the hot pressurized gases and protect the base material from environmental degradation. The coating may include one or more intermediate layers of metal and one or more outer layers of ceramic, which may be deposited to a final thickness of at least 0.13 mm (0.005 inches). It is therefore desirable that each of the cooling holes provided in the base material be protected during the application of the coating to avoid filling the holes or changing the shape of the hole exit regions.